Regeneration of decoked alkaline sulfite pulp liquor

ABSTRACT

DECOKED ALKALINE SULFITE PULP LIQUOR HAVING AN EXCESS OF SOLUBLE SULFITE IS REGENERATED BY TREATING WITH AN ALKALINE EARTH OXIDE AND/OR HYDROXIDE TO PRECIPITATE EXCESS SOLUBLE SULFITE ION AS INSOLUBLE ALKALINE EARTH SULFITE. THE SULFITE PRECIPITATE IS REMOVED BY FILTRATION AND THE RESULTING LIQUOR IS RECYCLED TO THE PULPING OPERATION. THE ALKALINE EARTH OXIDE AND SO2 ARE RECOVERED FROM THE FILTER CAKE BY HEATING.

United States Patent ice 3,761,349 REGENERATION 0F DECOKED ALKALINE SULFITE PULP LIQUOR Edward L. Cole, Fishkill, Howard V. Hess, Glenham, and William F. Franz, Gardiner, N.Y., assignors to Texaco Inc., New York, N.Y. No Drawing. Filed June 3, 1971, Ser. No. 149,863 Int. Cl. D210 11/02 US. Cl. 162-36 7 Claims ABSTRACT OF THE DISCLOSURE Decoked alkaline sulfite pulp liquor having an excess of soluble sulfite ion is regenerated by treating with an alkaline earth oxide and/or hydroxide to precipitate excess soluble sulfite ion as insoluble alkaline earth sulfite. The sulfite precipitate is removed by filtration and the resulting liquor is recycled to the pulping operation. The alkaline earth oxide and S0 are recovered from the filter cake by heating.

FIELD OF THE INVENTION This invention relates to a process for regenerating decoked alkaline sulfite pulp liquor from acid coking operation by treating with an alkaline earth oxide or bydroxide.

BACKGROUND OF THE INVENTION A process for coking waste alkaline sulfite liquor disclosed in commonly assigned copending application Ser. No. 149,425, filed even day herewith, is characterized by the step of acidifying the liquor with S0 in order to facilitate the coking as evidenced by being able to coke the lignins faster and at a lower temperature. The cokefree liquor resulting from the process contains valuable dissolved chemicals, the recycling of which to the pulping operation would enhance the economics of the whole process. This liquor however is acid and the alkaline sulfite wood pulping process desirably must be carried out at a pH of 9 to 12. An obvious way to render the decoked liquor suitable for reuse in the sulfite wood pulping process is to add enough sodium hydroxide thereto but this approach undesirably results in the build-up of both sodium hydroxide and sulfur as sulfite in the wood pulping system.

SUMMARY OF THE INVENTION It has now been discovered that decoked acid sulfite liquor may be regenerated by treatment with an alkaline earth oxide or hydroxide (the oxide or hydroxide of calcium being preferred) to precipitate the sulfite contained therein and to regenerate NaOH according to the following equation:

Nazsoa 011(011), 2NaOH+ 011503211201 (I) Filtration removes the CaSO -2H O and the resulting liquor is recycled to the pulping operation. Unslaked lime and S0 are recovered from the filter cake by dewatering and calcining in the presence of air to a temperature above 1200 F. but preferably in the range of 1500-2000 F., thus:

-250F 08.303.2Hg0 09.80: 21 2 3,761,349 Patented Sept. 25, 1973 Heating CaSO at a reduced temperature of 950 to 1200 F. will result in the following disproportionation:

The S0 is recycled to the coking step and the CaO is used in the treatment of the acid liquor in Equation 1.

The amount of alkaline earth oxide or hydroxide added to the acid decoked liquor will vary with the pH of this liquor. Generally, the amount will range from 5-50 grams Ca(OH) per liter of liquor in order to bring the liquor back to pH 7-12.

The use of Ca++ ion is preferred to the use of Ba++ or Mg++ because the former is less expensive; however, mixtures of the ions may be used; e.g., Mg++ and Ca++. The use of the calcium salt has the added advantage of lower solubility than either the salt of the other two alkaline earth metals, as indicated below:

Solubility in 100 parts The following examples are presented to illustrate more clearly the invention. The same, however, is not limited to these specific embodiments.

Example I shows the characteristics of a spent alkaline sulfite liquor and Example II shows the acidification of this spent liquor by the adsorption of S0 In Example III, the acid liquor from Example II was coked in the liquid phase to effect an 86% reduction in Total Organic Carbon in the liquid (filtrate). The washed and dry filter cake recovered has a low sodium content but a substantial sulfur content and heat of combustion. The cake can be advantageously burned for the recovery of heat and chemicals. The filtrate containing the bulk of the chemicals is acid, pH 4.4, and needs to be brought to the alkaline side prior to recycle.

Example IV shows that this was done by treating with slaked lime, thereby converting the liquor to a pH of 11.8 and removing excess SO ion, e.g.,

Red Heat CaSO; C S02 Example V shows that the recovered filtrate, even without refortifying was eifective in removing substantial quantities of the lignins from pine wood chips.

Ba(OH) was the alkaline earth hydroxide used in Example VI to eifect regeneration of the acid filtrate of Example III. A liquor having a pH of 11.9 was obtained.

Example VII shows that Mg(OH) was equally efleotive in altering the pH of Example III decoked waste liquor.

Sulfites are sensitive to oxidation by free oxygen to sulfates. Sulfates are an undesirable product in the process so care is exercised in the handling of the process liquid and alkaline metal sulfite to avoid contact with air.

3 EXAMPLE I A waste alkaline sulfite liquor gave the following analysis:

Sample number 1 Sulfur, wt. percent 1.59 Sodium, wt. percent 3.6 Calcium, wt. percent 0.05 Nitrogen, wt. percent 0.007 TOC, wt. percent 1 5.6 Ash, wt. percent 9.46 Dissolved solids, wt. percent 19.8 COD, g./l 156.5 pH 11.9

1 Total organic carbon.

Example II 1000 parts by weight of Sample 1 alkaline sulfite liquor, were placed in a vessel and S was slowly bubbled into the liquor. A total of 117 parts by weight of S0 were absorbed. The liquors pH now was 1.9 (Sample 2).

Example III 500 parts by weight of the Example II liquid (Sample 2) were placed in an autoclave. The autoclave was flushed with nitrogen and sealed. The autoclave was then heated to 552 F., and held at this temperature for two hours. A pressure of 1200 p.s.i.g. was generated. The autoclave was cooled to 80 F. and vented. A total of 3.8 parts by weight of gas was recovered (Sample 6). A total of 449 parts by weight of liquids and solids were recovered. Filtration yielded 378 parts by weight of light yellow liquid (Sample 3) and 68 parts by weight of wet filter cake. 34 parts by weight of the filter cake were dried on a steamplate to give 14.3 parts of dry cake (Sample 4). The outer 34 parts by weight portion of the filter cake were washed with 1000 parts of water and after drying on steamplate, 12.6 parts by weight of dry cake (Sample 5) were secured. Tests on the filtrate are as follows:

Sample: Filtrate Sample No 3 Sulfur, wt. percent 2.7 Sodium, wt. percent 3.7 Calcium, wt. percent 0.05 Nitrogen, wt. percent 0.002 TOC, wt. percent 0.8 Ash, wt. percent 12.6 Dissolved solids, wt. percent 12.9 COD, g./l. 28.1 pH 4.4; 4.5

Analysis of the filter cakes gave the following:

Unwashed Washed Sample dry cake dry cake Sample number 4 5 Sulfur, wt. percent 23. 3 31. 2

Sodium, wt. percent 4.3 0. 2

Ash, wt. percent 33. 8 16. 5

Gross heat of combustion, B.T.U./lb 6,988 8, 863

Tests on the gas stream from coking are as follows:

Sample No. 6 Thiophene mole percent 0.2 Dimethyl sulfide do 0.1 Methyl mercaptan do 0.5 CO do 81.3 H 5 do 15.2 H2 do 1.6 C -C do 0.9

Example IV 100 parts by weight of filtrate from Example III (Sample 3) reacted with 3.0 parts by weight slaked lime, Ca(OH) at room temperature. A precipitate formed that was filtered from the solution. 94.5 parts by volume of filtrate was collected (Sample 7) and 6.5 grams of filter cake. The latter contained 57 percent moisture.

The filter cake was placed in a glazed ceramic vessel and heated to red heat. During the heating process acid vapors were noted that were identified as S0 Ash, representing of the charge was recovered, and identified as Sample 9. Sample 9 has 10.7 weight percent of sulfur.

Example V 10 parts by weight pine wood chips were steamed in an autoclave at 350 F. and p.s.i.g. pressure for 15 minutes, cooled and allowed to drain to remove any excess water. 50 parts by volume of filtrate (Sample 7) from Example IV was added to the steamed wood chips contained in the autoclave. The autoclave was then heated to 340-350 F., the wood chips allowed to digest at this temperature for 90 minutes; cooled and the pulp was withdrawn from the digester. The pulp was washed and dried to recover 7.4 parts by weight of dry paper pulp (i.e., equal to 26 weight percent loss of lignins) and 49 parts by weight of liquid having a dark brownish color (Sample 10). Sample 10 had a pH of 6 and a COD of 4430 mg. 0 /1.

Example VI 25 parts by weight of filtrate from Example III (Sample 3) was reacted with 3.5 parts by weight of Ba(OH) at room temperature. The reacted product was filtered to give 23.2 parts by volume of filtrate and 5.0 parts by weight of wet filter cake. The latter contained 63.5 percent moisture.

Dry filter Sample Filtrate cake Sample number 11 12 Barium, wt. percent 53. 5 Sulfur, wt. percent. 2. 00 3. 9 Sodium, wt. percent 3.91 2. 26 D, g. 18. 4 pH 11. 9

Wt. percent Sulfur 4.7 Barium 53.9 Sodium 2.2

Example VII 25 parts by volume of filtrate from Example III (Sample 3) was reacted with 1.5 grams Mg(OH) at room temperature. The reacted product was filtered to give 23.6 parts by weight of filtrate (Sample 14) and 2.8 parts by weight of Wet filter cake. The latter contained 52 percent moisture.

Dr filter Sample Filtrato y cake Sample number 14 15 Sulfur, wt. percent" 2. G7 10. 1 Sodium, wt. percent. 3.82 6. 3 COD,g./l 11.3 pH 11. 9

A portion of the wet filter cake was placed in a glazed ceramic vessel and heated rapidly to a red heat. During the heating process acid vapors were noted that were Wt. percent Sulfur 9.3 Sodium 5.2

What is claimed is:

1. In a process for the regeneration of pulp liquor wherein the liquor is acidified with S coked to produce an alkaline sulfite pulp liquor and coke, and the alkaline sulfite pulp liquor and coke are separated, the steps of: treating the acidified, separated liquor with an amount of alkaline earth metal oxide or hydroxide sufiicient to bring the pH of said liquor to between about 7 and 12, and to form an alkaline earth metal sulfite separating the alkaline earth metal sulfite from said liquor, recycling said liquor to pulping operation, and heating said alkaline earth metal sulfite to about 1200 F. to form the corresponding alkaline earth metal oxide and sulfur dioxide, said steps being carried out substantially in the absence of air to avoid oxidation of sulfites to sulfates.

2. The process according to claim 1 wherein said alkaline earth metal sulfite is heated to a temperature of between about 1200 F. and 2000 F.

3. The process according to claim 1 wherein said alkaline earth metal oxide obtained by heating said sulfite is used in treating said liquor.

4. The process according to claim 1 wherein said alkaline earth metal oxide or hydroxide is calcuirn oxide or hydroxide.

5. The process according to claim 1 wherein said alkaline earth metal oxide or hydroxide is barium or magnesium oxide or hydroxide.

6. The process according to claim 1 wherein there are used from 5 to grams of calcium hydroxide per liter of liquor.

7. The process according to claim 1 wherein a mixture of alkaline earth metal oxides or hydroxide is used to treat the liquor.

References Cited UNITED STATES PATENTS 2,750,290 6/ 1956 Schoeffel 210-50 X 2,752,243 6/1956 Barton et al. 162-31 2,716,589 8/1955 Byrns 162-36 X 2,801,900 8/1957 Benning et al 423-512 X S. LEON BASHORE, Primary Examiner A. DAANDREA, JR., Assistant Examiner US. Cl. X.R. 

